An A320 flight crew reported a probable wake turbulence encounter at FL370 that resulted in signific...

Narrative:

We were at FL370 (approx); autopilot was on; weather was clear; visibility unlimited; smooth air. Suddenly; for no apparent reason; the aircraft banked approx 25-30 degrees right; then went about 20 degrees left. The autopilot did not disengage; but I disengaged it manually and maintained level flight with aileron input only. After both pilots confirmed that all flight computers were functioning normally; I re-engaged the autopilot. All flight phases were uneventful after I re-engaged the autopilot. Everything was functioning normally. It was at this time that the first officer (pilot not flying) noticed a spiraling shaped vortex at our flight level. To me; it looked like wing tip vortices. It was there momentarily; and; after a brief discussion; we determined the vortex to possibly be some wake turbulence (like one would see on final approach or while observing landing aircraft) from another aircraft. I then made an announcement to the passengers about our circumstance; and then I talked with the chief purser on their experiences in the passenger compartment. Though everyone was startled; all flight attendants were ok as well as all of the passengers. There were no reports of any injuries; though I was told one woman in the back was crying. As turbulence is a 'part of the job' and because no passenger or flight attendant was injured; both pilots decided that a report was unnecessary for this incident. In retrospect; I believe I should have informed ATC and asked if there were any large/heavy aircraft near our plane that may have caused our temporary problem with their wake; but we did not elect to do this. Finally; I made it a point to go out in the cabin during deplaning to address any passenger concerns or questions. I received no negative comments about our flight; only praise.

Original NASA ASRS Text

Title: An A320 Flight Crew reported a probable wake turbulence encounter at FL370 that resulted in significant uncommanded roll in both directions. The crew reported what appeared to be spiral-shaped wing tip votices at their flight level.

Narrative: We were at FL370 (approx); autopilot was on; weather was clear; visibility unlimited; smooth air. Suddenly; for no apparent reason; the aircraft banked approx 25-30 degrees right; then went about 20 degrees left. The autopilot did not disengage; but I disengaged it manually and maintained level flight with aileron input only. After both pilots confirmed that all flight computers were functioning normally; I re-engaged the autopilot. All flight phases were uneventful after I re-engaged the autopilot. Everything was functioning normally. It was at this time that the First Officer (pilot not flying) noticed a spiraling shaped vortex at our flight level. To me; it looked like wing tip vortices. It was there momentarily; and; after a brief discussion; we determined the vortex to possibly be some wake turbulence (like one would see on final approach or while observing landing aircraft) from another aircraft. I then made an announcement to the passengers about our circumstance; and then I talked with the Chief Purser on their experiences in the passenger compartment. Though everyone was startled; all Flight Attendants were OK as well as all of the passengers. There were no reports of any injuries; though I was told one woman in the back was crying. As turbulence is a 'part of the job' and because no passenger or Flight Attendant was injured; both pilots decided that a report was unnecessary for this incident. In retrospect; I believe I should have informed ATC and asked if there were any large/heavy aircraft near our plane that may have caused our temporary problem with their wake; but we did not elect to do this. Finally; I made it a point to go out in the cabin during deplaning to address any passenger concerns or questions. I received no negative comments about our flight; only praise.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	893570
Time
Date	201005
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 210 Flight Crew Total 30000 Flight Crew Type 4000
Person 2
Function	First Officer Pilot Not Flying
Experience	Flight Crew Last 90 Days 230 Flight Crew Total 13000 Flight Crew Type 7000
Events
Anomaly	Inflight Event / Encounter Wake Vortex Encounter

An A320 flight crew reported a probable wake turbulence encounter at FL370 that resulted in significant uncommanded roll in both directions. The crew reported what appeared to be spiral-shaped wing tip votices at their flight level.